Analysis and design of gradient descent based pre-synchronization control for synchronverter

Synchronverter (SV) control has emerged as a popular method for distributed energy resources (DERs), to emulate response of a synchronous generator. In this work, a simple gradient descent based pre-synchronization control for SV scheme is proposed that varies the reference frequency in SV control alone. Thus, local load connection to DER can remain intact during synchronization with proposed pre-synchronization method, unlike virtual current based methods. Normally, phase-locked loop used for synchronization purpose, uses a first order loop filter such as a PI controller. In the proposed pre-synchronization control, the inherent low pass filter of SV scheme itself is used as a loop filter. Transient response analysis is presented in this work, based on small signal transfer functions derived from the proposed method. From the theoretical analysis of proposed pre-synchronisation control, design of the parameters is presented. Thus, there is no trial and error basis for parameters tuning in the proposed method, as compared to virtual current based methods. Validation of proposed pre-synchronisation control through experiments are presented for all initial conditions. The transient response analysis, effectiveness of proposed method during local load changes and grid integration are verified by experimental results.